The present invention relates to an electromagnetic actuator for the actuation of the valves of an internal combustion engine.
As is known, internal combustion engines are currently being tested in which the intake and exhaust valves that selectively bring the combustion chamber of the engine into communication with the intake manifold and respectively with the exhaust manifold of the engine are actuated by electromagnetic actuators driven by an electronic control unit. This solution makes it possible to vary, in a very precise manner, the lift, opening time, and opening and closing moments of the valves as a function of the angular speed of the crankshaft and of other operating parameters of the engine, substantially increasing the performance of the engine.
The electromagnetic actuator that currently provides the best performance is disposed alongside the stem of the valve of the internal combustion engine to be axially moved and comprises a support frame rigid with the head of the internal combustion engine, an oscillating arm of ferromagnetic material having a first end hinged on the support frame in order to be able to oscillate about an axis of rotation perpendicular to the longitudinal axis of the valve, and a second cam-shaped end disposed in abutment on the upper end of the stem of the valve, and a pair of electromagnets disposed on opposite sides of the central portion of the oscillating arm in order to be able to attract, on command and alternatively, the oscillating arm by causing it to rotate about its axis of rotation.
Each electromagnet is normally formed by a magnetic core formed by a pack of sheets clamped between two lateral metal plates forming part of the support frame and by a coil of electrically conducting material keyed on the magnetic core.
The electromagnetic actuator lastly comprises two elastic members, the first of which is adapted to maintain the valve of the engine in a closed position and the second of which is adapted to maintain the oscillating arm in a position such as to maintain this valve in the position of maximum opening. The two elastic members act in opposition against one another and are dimensioned such as to position, when neither of the electromagnets are being supplied, i.e. they are in a condition of equilibrium, the oscillating arm in a rest position in which it is substantially equidistant from the polar heads of the two electromagnets so as to maintain the valve of the engine in an intermediate position between the closed position and the position of maximum opening.
The main drawback of the electromagnetic actuator described above is that there is mechanical play between the cam-shaped end of the oscillating arm and the upper end of the stem of the valve which varies substantially as a function of the operating temperature of the actuator, thereby ruling out some of the advantages deriving from the use of such an electromagnetic actuator. The lift of the valve, the opening time and the moments of opening and closing of the valves in practice vary substantially as a function of the mechanical play between the cam-shaped end of the oscillating arm and the upper end of the stem of the valve, substantially reducing the actuation precision that can be obtained when using the above- mentioned electromagnetic actuator.
In the electromagnetic actuator described above it is also very important for the packs of sheets of each electromagnet always to maintain their optimum predetermined position in which the air gaps between the sheets are reduced to a minimum. This is necessary because the consumption of electrical energy by the two electromagnets has to be minimised, and in practice the greater the air gaps of the magnetic circuit, the greater the magnetising currents that have to circulate in the electromagnets and therefore, the greater the power used and the power dissipated by these electromagnets. Reducing the air gaps to a minimum requires highly accurate assembly of the components of the magnetic circuit (substantially the electromagnets and the oscillating arm) and this assembly precision has to be maintained over time during the normal operation of the actuator, and therefore any variations of the optimum position of the packs of sheets (due to displacements and/or deformations of the plates as a result of mechanical stresses) may readily entail an overall increase of the air gaps.
The object of the present invention is to provide an electromagnetic actuator for the actuation of the valves of an internal combustion engine that makes it possible to recover the mechanical play and that, at the same time, makes it possible to maintain the packs of sheets forming the magnetic core of each electromagnet in the above-mentioned predetermined optimum position.
The present invention therefore relates to an electromagnetic actuator for the actuation of the valves of an internal combustion engine that comprises a head, at least one variable- volume combustion chamber, at least one connection duct adapted to bring the combustion chamber into communication with atmosphere, and at least one valve adapted to regulate the passage of fluids to and from the combustion chamber, the valve being mounted in the head such that it can move axially between a closed position in which it closes off the connection duct and a position of maximum opening in which it enables fluids to pass through the connection duct with the maximum admissible flow, the electromagnetic actuator being mounted on the head in order to move the valve, on command, between its closed position and its position of maximum opening and being characterised in that it comprises means for recovering the mechanical play existing between the valve and the actuator.